Confessions of a Recovering Thickie

[ZeeOSix]

To me, it just comes across as “how thin can we go” ...

CAFE try outs by engine lubrication design engineers ...

 

[siriusc1024]

Yup, properly functioning cooling system will take care of those few extra 2-3F. Also, Honda DI dilutes oil with fuel and viscosity drops by 2 cSt+, this is where extra “safety margin” can come handy. I think of it as an insurance. The worst thing that can happen is you will spend few more dollars on gas…

Especially with the ridiculous OCI's manufacturers claim.

 

[siriusc1024]

Further, I'll argue that people getting away with running viscosities way higher than spec are doing so due to additives that come into play to mitigate metal-metal contact.

Long term, this will decrease the life of the engine.

 

[ZeeOSix]

Further, I'll argue that people getting away with running viscosities way higher than spec are doing so due to additives that come into play to mitigate metal-metal contact.

Long term, this will decrease the life of the engine.

LoL ... you have it backwards. Thinner oils rely more on AF/AW additives to mitigate wear when he MOFT is too small and goes to zero. Those additives is what gives the oil its "film strength" to provide the wear mitigating tribofilm on rubbing surfaces. Guess you didn't read that Machine Lubrication article I linked for you in the other thread. Here it is again. Film thickness (MOFT) is the main wear prevention factor, and the AF/AW tribofilm (film strength) is the backup mechanism that takes over to prevent wear when the MOFT goes to zero. Thicker oil does not cause more wear, but thinner oil can as has been shown in many ways, yet you keep coming up with whatever misconception you can to convince yourself into believing less viscosity is better than not. Did you go to the SubsTech website and read up on jourmal bearings?

https://www.machinerylubrication.com/Read/30835/lubricant-film-strength

 

[siriusc1024]

I just described to you that film thickness changes with dynamic loading. The lubricant has to allow for quick formation of they hydrodynamic wedge that will have a different profile for different loads.

Too thick oil can result in metal-metal contact because the hydrodynamic wedge is too slow to adapt to the transient.

When that breaks down all you have left is the additives to mitigate the metal-metal contact. It's completely irrelevant which type has what add-pack to the fact that the film has broken down.

I have nothing backwards. Dynamic vs static. You're thinking static loading. Dynamic is the prevailing condition in engines.

 

[ZeeOSix]

I've found an instance where increased viscosity can result in wear. So far, the evidence presented that higher viscosity means higher MOFT has depended on a system where the load is static - not changing.

Nope, you don't understand that the MOFT in journal bearings (and all other moving parts) changes based on their RPM or speed of the two sufaces past each other (that's basic Tribology), so MOFT is a dynamic parameter ... not static as you claimed.

Consider dynamic loading of a sleeve bearing. Higher viscosity oil may result in metal-metal contact during dynamic loading.

In a dynamic loading situation, MOFT is related to both viscosity and clearance!

1. The clearance between the journal and bearing narrows quickly due to:​

• A load spike
• Shaft deflection
• Shock or vibration

These cause the bearing surfaces to approach each other very quickly, reducing film thickness rapidly.

2. Because the surfaces are converging, the lubricant film gets thinner, and pressure is generated by forcing the oil sideways through the narrowing wedge.​

This is the squeeze film effect.

For the squeeze film to protect the surfaces, it must respond immediately by building pressure as the gap closes.

3. If oil can flow quickly enough (low viscosity), a hydrodynamic pressure field develops in the narrowing film to push back against the load.​

This pressure supports the journal and prevents contact.

Why High-Viscosity Oil Is Slower​

A high-viscosity oil resists being squeezed and flowing laterally due to:

• Greater internal friction.
• Greater resistance to shearing.

So when the surfaces approach quickly:

• The oil doesn't flow fast enough to spread pressure.
• As a result, the pressure lags behind the motion.
• The minimum film thickness is reached before pressure can build enough.
• This leads to film collapse.

In such a rapid event:

• High viscosity resists fluid movement, which is needed to form the pressure field in the squeeze film.
• The time lag in redistributing the oil (due to inertia and flow resistance) means the pressure doesn’t build up fast enough.
• By the time sufficient pressure is formed, the surfaces may already be too close, risking boundary contact or metal-to-metal friction.

This is an issue of hydrodynamic delay.

Another big cherry pick. Do you really think something like that is a big concern when there are all kinds of engine OMs, just like for your Rouge engine in other countries, show that anything from xW-20 to xW-50 can be used? And millions of vehicles are cruising around every day using oil much thicker than xW-20 or less. For an ICE to do that, like due to some crazy LSPI event, that's going to happen no matter what viscosity is being used. The piston ring lands will be blow to pieces and the rod bent or sent through the block, so who cars what happened to the rod bearings, lol.

 

[siriusc1024]

Nope, you don't understand that the MOFT in journal bearings (and all other moving parts) changes based on their RPM or speed of the two sufaces past each other (that's basic Tribology), so MOFT is a dynamic parameter ... not static as you claimed.


Another big cherry pick. Do you really think something like that is a big concern when there are all kinds of engine OMs, just like for your Rouge engine in other countries, show that anything from xW-20 to xW-50 can be used? And millions of vehicles are cruising around every day using oil much thicker than xW-20 or less. For an ICE to do that, like some crazy LSPI event, that's going to happen no matter what viscosity is being used.

That's not dynamic loading. Force driving the surfaces together is loading. Force changing is dynamic.

Everything can't be a cherry pick just because you don't like it. You're being obstinate and ignoring the math. Like you put it to me, you need to study on journal bearings. I posted the links.

The allowance for higher viscosity oil is temperature dependent. Think about it.

 

[siriusc1024]

The below is a bunch of AI search result garbage - I know the search result format. If the MOFT is larger and the oil more viscous, then it's going to support the bearing better in a shock load event. Go read the SubsTech website about the load distribuion isnide the bearing as a function of vicosity and bearing clearnace. The thicker oil already provides a more uniform pressure distributiion to start with. A bearing with thinner oil will have a more ununiform pressure distribuition, therefore is will be more sensitive to shock loading and lose more MOFT (and it was already a thinner MOFT to start with) than a more even pressure distributiion of the supporting wedge from thicker oil.

So if thicker oil is causing all of this to happen then why is about every high performance engine specifying thicker oil, and also why is thicker oil used in cars in track events? And why are those darn Nissan engineers saying taht20W-50 can be used in a Rouge?

Now it's cherry picked garbage. "La-la-la I can't hear you."

Because at the track the temps are higher. Same for higher ambient temps.

Go ahead and plot some viscosities vs temp. x-axis 200F to 350F. Draw a line straight across. There's what temp the oil need to be to have equivalent effective viscosity.

20w-50 in something spec'd 0w-20 is dumb. Only way it works is if the oil is much hotter.

Within the normal operation envelope, running thick oil in a tight clearanced engine spec'd for light oil may increases the risk of metal-metal contact.

MOFT in a dynamic situation is related to clearance. If the oil is too thick it can't flow in a tighter clearance to maintain MOFT as the load changes.

 

[ZeeOSix]

That's not dynamic loading. Force driving the surfaces together is loading. Force changing is dynamic.

Yeah, I gave you a good example of shock loading ... LSPI. To be clear, yes the rod bearings do get "dynamic" loading in normal use due to the combustion on the piston, and the recipricating mass of the piston and rod. And to reiterate, the MOFT inside the bearing changes from all kinds of factors - viscosity, bearing speed, bearing clearance.

Everything can't be a cherry pick just because you don't like it. You're being obstinate and ignoring the math. Like you put it to me, you need to study on journal bearings. I posted the links.

No, I'm ignoring information that doesn't agree with many other sources on journal bearings. Go learn more about them instead of searching for something that you think fits your narritive that thinner oil is better for engine protection than thicker oil. All the info I've shown in this thread shows thinner KV100/HTHS viscosity doesn't give any added protection. All it does is reduced friction and give a hair more fuel economy. It can also cause more wear compared to using a thicker oil ... depends on the engine and use conditions.

The allowance for higher viscosity oil is temperature dependent. Think about it.

Yeah, but do you know that the root reason is due to oil temperature? Again, it's all about MOFT ... always has been ever since two surfaced were moving with oil between them.

 

[siriusc1024]

Yeah, I gave you a good example of shock loading ... LSPI. To be clear, yes the rod bearings do get "dynamic" loading in normal use due to the combustion on the piston, and the recipricating mass of the piston and rod. And to reiterate, the MOFT inside the bearing changes from all kinds of factors - viscosity, bearing speed, bearing clearance.


No, I'm ignoring information that doesn't agree with many other sources on journal bearings. Go learn more about them instead of searching for something that you think fits your narritive that thinner oil is better for engine protection than thicker oil. All the info I've shown in this thread shows thinner KV100/HTHS viscosity doesn't give any added protection. All it does is reduced friction and give a hair more fuel economy. It can also cause more wear compared to using a thicker oil ... depends on the engine and use conditions.


Yeah, but do you know that the root reason is due to oil temperature? Again, it's all about MOFT ... always has been ever since two surfaced were moving with oil between them.

NASA

It is MOFT. YES! MOFT must be maintained as load changes. As the load changes the shape of the hydrodynamic wedge changes. Thicker fluids aren't as responsive to changes. That's not hard to figure out!

I'm not making a general statement about any viscosity. The narrative is that an engine is designed with a viscosity in mind. I showed how MOFT is related to bearing clearance and viscosity.

 

[ZeeOSix]

Now it's cherry picked garbage. "La-la-la I can't hear you."

Because at the track the temps are higher. Same for higher ambient temps.

Go ahead and plot some viscosities vs temp. x-axis 200F to 350F. Draw a line straight across. There's what temp the oil need to be to have equivalent effective viscosity.

You're telling me something I've known for decades. Are you just now learning about this stuff after you saw the EE video showing that viscosity vs temp graph. Yes, you finally figured out why thicker oil is used for track use and any other use condtion where the oil might get hotter. You think using 0W-20 on the track is a good idea now, lol?

20w-50 in something spec'd 0w-20 is dumb. Only way it works is if the oil is much hotter.

Yes of course 20W-50 is going to work better when hotter. Sure, it's probably not necessary for "normal" driving to the grocery store. BUT, it could be used ... just like the Nissan engieers say so in the OM. That's for the owner of the vehcle to decide. But again, the thicker oil is still going to provide more engine protection headroom. Why is it so hard to undertand headroom, and why some people might want that.

Within the normal operation envelope, running thick oil in a tight clearanced engine spec'd for light oil may increases the risk of metal-metal contact.

No it won't, if you really understood journal bearings. Again, if that was the case then every car in Alaska, Minnisota and similar super cold climates would all have damaged bearings. They don't. Need some simple logic to know even that tight bearings (0.001 to 0.002 in clearance as already shown) don't car about thicker oil. Cold start-up and engieers specing 20W-50 in OMs proves that.

MOFT in a dynamic situation is related to clearance. If the oil is too thick it can't flow in a tighter clearance to maintain MOFT as the load changes.

Wrong, see the response directly above. Go study journal bearings a bunch, and you might cure your misconcetions about this stuff.

 

[siriusc1024]

I've know forever that viscosity is related to temp. That's why I always roll my eyes when people say if they can use it at the track it'll work on the street. The Nissan recommendation scales with ambient temps. That means higher oil temps. Grades are separated by 20-40F above 212F depending on VI. If you're in a situation where oil temps are approaching 300F instead of a normal 220F then go up 2 grades. Rough example.

The asinine false equivalence of cold Alaska speaks more to making sure you warm up the engine before getting on it, which we all know to do.

I'm not saying catastrophic failure. Never have. Increased wear over time, absolutely.

Specifically, which part of what I posted do you contend? The math, references, or description?

 

[ZeeOSix]

NASA

It is MOFT. YES! MOFT must be maintained as load changes. As the load changes the shape of the hydrodynamic wedge changes. Thicker fluids aren't as responsive to changes. That's not hard to figure out!

Don't think so. The viscosity difference between the KV100 of xW-8 to xW-60 isn't so huge that bearings are going to experience this supposed phenomena. Besides, if this was actually going on in ICE engines, the bearings would be destroyed on cold start-up when the viscosity is literally a 1000 times more viscous. Critical logic ... do you really think engines would even be using xW-50 if this was going on and smoking bearings, lol?

Link up the actual study, not the AI search result.

I'm not making a general statement about any viscosity. The narrative is that an engine is designed with a viscosity in mind.

How can you keep stating this after 19 pages of discussion about journal bearing operation?

I showed how MOFT is related to bearing clearance and viscosity.

You did? But you seem to not still understand it even after all this discussion and the info posted from SubsTech/King Bearing's information. King Bearings has lots of expertise on bearings - did you go there yet .. if not you should.

 

[siriusc1024]

Please post that king bearing graphic again for context. I'll show you.

 

[chris719]

Don't think so. The viscosity difference between the KV100 of xW-8 to xW-60 isn't so huge that bearings are going to experience this supposed phenomena. Besides, if this was actually going on in ICE engines, the bearings would be destroyed on cold start-up when the viscosity is literally a 1000 times more viscous. Critical logic ... do you really think engines would even be using xW-50 if this was going on and smoking bearings, lol?

Link up the actual study, not the AI search result.


How can you keep stating this after 19 pages of discussion about journal bearing operation?


You did? But you seem to not still understand it even after all this discussion and the info posted from SubsTech/King Bearing's information. King Bearings has lots of expertise on bearings - did you go there yet .. if not you should.

GM even invalidates everything he claims by running 0W-40 from factory in the LT engines with same bearing clearances and recommending it for the “bad” engines. It’s pretty clear that GM should be running 0W-40 in these engines because the nearly identical LT engines in the lower volume Camaro and Corvette run it. The answer as we all know is $$$. Even if the failures are from defects at the end of the day, if you can’t ensure QC compatible with your aggressive viscosity selection maybe you should reconsider.

Separately, the takeaway of that video is pretty funny because how could you believe that GM engineer that their validation was sufficient if it allowed for a problem that affects 800k engines. Either the engines are bad and no oil will fix it, or the engines are not bad and your oil validation protocol is not conservative enough.

 

[ZeeOSix]

I've know forever that viscosity is related to temp. That's why I always roll my eyes when people say if they can use it at the track it'll work on the street.

They are right actually. The Nissan OM for your Rouge in EU/Thailand shows that. Maybe they should roll their eyes when you tell them thinner oil will protect their engine better.

The Nissan recommendation scales with ambient temps. That means higher oil temps. Grades are separated by 20-40F above 212F depending on VI. If you're in a situation where oil temps are approaching 300F instead of a normal 220F then go up 2 grades. Rough example.

Go look at the Nissan OM oil chat again. All the viscosities go up to the same max temp of the chart of 104F and above. The only thing that says you can't use a certain W grade is the lower ambient temps on the chart.

Where you coming up with this "Grades are separated by 20-40F above 212F depending on VI" claim?

The asinine false equivalence of cold Alaska speaks more to making sure you warm up the engine before getting on it, which we all know to do.

Guess you don't understand the significance of the W grade either. There's more to just "warming up the engine before getting on it" involved with super cold winter start-up. There were mega-threads all about W grade and cold cranking and pumpability of the oil. Go do some research on why SAE J300 came up and developed the W grade specifications - it's pretty interesting actually. They weren't pulled out of the air or some rabbit hole.

I'm not saying catastrophic failure. Never have. Increased wear over time, absolutely.

If the W grade is way off, there certainly be catastrophic failure. Again, why SAE J300 has defined W grades to what they are today.

Specifically, which part of what I posted do you contend? The math, references, or description?

About everything ... isn't it obvious?

 

[ZeeOSix]

Please post that king bearing graphic again for context. I'll show you.

Which one? You gonna show me what?

 

[siriusc1024]

Which one? You gonna show me what?

That's why I want it here. Had to go searching. The one from post 326.

 

[ZeeOSix]

GM even invalidates everything he claims by running 0W-40 from factory in the LT engines with same bearing clearances and recommending it for the “bad” engines.

Separately, the takeaway of that video is pretty funny because how could you believe that GM engineer that their validation was sufficient if it allowed for a problem that affects 800k engines. Either the engines are bad and no oil will fix it, or the engines are not bad and your oil validation protocol is not conservative enough.

Yeah, I'm thinking some of both, ie, a design/manufacturing problem and not a very good validation of adequate oil viscosity to cover all possible owner driving conditions. Bet their specifying xW-20 caught up to them over time. Who knows, maybe most of the engines that didn't show an issue had thicker oil in them because the owners knew simple Tribology and understood that going up a grade would add protection. It's similar to the KIA debacle where they started using some engine monitoring system to detect bearing failure, then went up in viscosity too.

 

[siriusc1024]

GM even invalidates everything he claims by running 0W-40 from factory in the LT engines with same bearing clearances and recommending it for the “bad” engines. It’s pretty clear that GM should be running 0W-40 in these engines because the nearly identical LT engines in the lower volume Camaro and Corvette run it. The answer as we all know is $$$. Even if the failures are from defects at the end of the day, if you can’t ensure QC compatible with your aggressive viscosity selection maybe you should reconsider.

Separately, the takeaway of that video is pretty funny because how could you believe that GM engineer that their validation was sufficient if it allowed for a problem that affects 800k engines. Either the engines are bad and no oil will fix it, or the engines are not bad and your oil validation protocol is not conservative enough.

Because it didn't affect L87's prior to 2021. Because warranty replacements are spec'd back to 0w-20, and the warranty is extended to 150k/10yr.